I wanted to keep this post separate from the ‘make mercs cheaper’ demands going on in other threads, so here it is.
I don’t believe I have seen anything like this idea so far on these forums, please correct me if I am wrong.
During a merc rotation there are two mercs free to use for the community, whether or not they have purchased that merc. They can use that merc until the rotation changes. During that time they may have crafted a card for that merc or even gotten a decent card from a case. During the week of rotation a casual player most likely didn’t earn enough to purchase that merc. After the rotation changes they are stuck with a useless card(unless to turn it into something else) until that merc goes on rotation again, which currently has no schedule or early announcement.
My idea is to discount the credit price of any merc used while it was on rotation equal to the amount of credits earned while playing that merc up to 50% of the price. This can effectively make a merc half price for a player that likes to play it and wants it after trying it out for a week and if the 50% off mark is achieved then the player is guaranteed to have earned the remaining cost during playtime. They could buy it before the 50% mark is reached for whatever discount they did earn.
Discount=CreditsEarnedAs/CreditPrice
If Discount>0.5 then Discount=0.5
FinalPrice=Discount*CreditPrice
I am aware that this is super simple math and that ANY instance of credit earn equal to or below 50% of the merc price will result in a discount equal to the amount of credits earned. The 2nd step was added to ensure that no additional discount will be mistakenly awarded to a player. Also, if this idea is at all accepted(completely unlikely) then the discount could be capped at a lower rate, as that is a decision to be made by the people in charge of monetization.
As an alternative, this same equation could be used to determine a real money discount instead of/in addition to a credit discount.
Please post any thoughts you might have. This is simply a suggestion that is HIGHLY DOUBT will be added to the game. Tear it apart at will and correct any mistakes you may see, but please don’t turn this thread into an argument. 
Thanks and Happy Fragging